The invention relates to an electroluminescent element having a transparent substrate which is provided with a layer of electroluminescent material between a first transparent electrode layer and a second electrode layer, and connections for the electrodes. The invention also relates to a display device with at least a pixel comprising such an electroluminescent element. The invention further relates to a radiation source, for example, an illumination source comprising such an electroluminescent element.
When used in a display device, an electric current flows from the first electrode layer to the second electrode layer during use, for example, within windows defined by a layer of insulating material. Dependent on the drive, the layer of electroluminescent material then luminesces in accordance with the windows defined in the layer of insulating material. Fixed patterns (icons or segments) can thus be displayed. It is alternatively possible to adapt the display device as a matrix display in which the layer of insulating material is usually absent. Pixels are then defined by overlapping parts of the first electrode layer and the second electrode layer. In the latter case, active drive is also possible.
The layer of electroluminescent material usually comprises a layer of organic material (for example, poly(p-phenylene vinylene) or PPV).
An electroluminescent element of the type described in the opening paragraph is used in the display device described in PCT application WO 96/36959 (PHN 15.320). In this display device, pixels are defined by the overlapping parts of the first and the second electrode layer. The layer of electroluminescent material comprises a semiconducting layer (active layer) and a hole-injecting electrode, which form diodes at the location of the pixels. During selection of a row of pixels, one or more diodes within a row convey current due to the presented drive signals, and luminesce. The light level is initially determined by the (adjustable) current through the pixel. Upon selection of a plurality of pixels within a row, a problem may occur when there is a short circuit within one of the pixels (or is caused during use) between the first and the second electrode layer. Since substantially all of the current now flows through the associated short-circuited diode, diodes associated with other pixels in the same selected row will not convey current or hardly convey current and will therefore not luminesce.
It is an object of the present invention to at least partly eliminate the above-mentioned problem.
To this end, an electroluminescent element according to the invention is characterized in that the electroluminescent element comprises a plurality of sub-elements in electrically parallel-arranged branches, and, in each branch, a fuse element between one of the connections and a part of the layer of electroluminescent material. The material of the electrode layer can then also be used as a material for the fuse element.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.